© Isothermal Technology
Page 60 of 102
923 milliK manual - issue: 1.10
100mV on the 115mV range
10mA on the 30mA range
A known temperature measured using a thermocouple and internal reference junction
compensation
The measurements should be made independently on both channels.
5.2.1 PRT/SPRT Resistance Range
Checking the resistance ranges used for PRT/SPRTs (115
Ω
and 460
Ω
) involves checking the
values indicated at zero (0
Ω
) and approximately full-scale (100
Ω
and 400
Ω
) on both
channels.
5.2.1.1
PRT/SPRT Resistance Range – Zero Check
The current reversal employed by the milliK eliminates the effect of thermal EMFs and
provides an inherently stable zero for resistance measurement. There is therefore no zero
adjustment for resistance and the zero check is only used to confirm correct operation of the
milliK.
Apply a 4-terminal short–circuit (see section 5.1.1) to channel 1 and set the milliK to read its
resistance on the 115
Ω
range at 1mA by changing the parameters in the
Settings
Window:
Next, press the
Numeric
(F2) key, clear the statistics and wait for 100 measurements to be
made (when the display shows “Mean of 100”). The specification states that the accuracy
across the range should be within ±7ppm of range, which equates to 0.00080
Ω
, however this
zero reading should be <±0.00010
Ω
. After checking the zero-ohm reading on channel 1,
repeat the measurement on channel 2. There is no adjustment possible for zero resistance
